And on March 18, “Bates Motel,” a modern-day prequel to Alfred Hitchcock’s “Psycho,” debuts. The A&E series chronicles the formative relationship between a teenage Norman Bates (Freddie Highmore) and his controlling mother (Vera Farmiga).

Psychopaths aren’t new fodder for American television. One of the highest-rated two-part made-for-TV films ever, 1976’s disturbing “Helter Skelter,” graphically chronicled the real-life 1969 murder spree by Charles Manson and his “family” of followers. Many series since then — including “Nip/Tuck,” “CSI,” “Criminal Minds” and “The Mentalist” — have offered episodes centering on serial killers.

But only since 2006, when Michael C. Hall’s blood-soaked vigilante Dexter Morgan started slicing his way through Miami on Showtime’s “Dexter,” have series elevated the serial killer to lead character.

Where does this seemingly sudden fascination with the genre come from?

“I think we always like a boogey monster of some kind. We see these tropes come up now and then,” says Purefoy, the British actor whose cutting stare befits his Edgar Allan Poe-fixated killer, who ritually excises his victims’ eyeballs on “The Following.”

“We had vampires for three or four years. Now we’ve also got zombies on ‘The Walking Dead,’” he says. “But those characters are fictitious. Serial killers are very real, and they can be in the grocery store, in line at the bank, on the subway,” he adds. “It’s a creepy idea that they are out there amongst us.”

Leonard Cassuto, a professor of English at Fordham University who has studied fictional depictions of serial killers, agrees. “The thing about the serial killer story is that they’re everywhere and they’re nowhere — they hide amongst us. They are a kind of monster who we cannot distinguish,” he says. “What about the monster who looks just like the person next door?”

Best-selling author Jeff Lindsay, author of the “Dexter” novels that inspired the series, crafted his boyish protagonist with that in mind. But he also took pains to make him otherwise approachable.

“I deliberately wrote it in the first person so [the character] would be easier to get close to — and people do,” he says of the technique that also pops up in the show by way of Hall’s voice-over narration. “People get into his head and go, ‘You know, he’s not so bad,’” he says, adding, “He’s very, very, very bad — but he’s on our side.”

Lindsay, who is currently working on a seventh “Dexter” novel that will be published next fall, also says there’s “no question” that audiences have grown more desensitized to blood and violence (and, in fact, he says the televised Dexter is “a lot more graphic” than his books). One of the other ways he was able to make Dexter acceptable as a lead character was to make him “deliberately funny. I sort of wanted to play with that reaction of ‘This should be shocking you,’” he says. “I had a directing teacher who called it the ‘illegal laugh.’”

Marcos Siega, executive producer of “The Following,” directed nine episodes of “Dexter” and sees that series as a game-changer for viewers. He thinks that audiences can better appreciate a reprehensible character.

“Certainly with cable there’s been a lot of shows — ‘The Sopranos,’ ‘Dexter,’ ‘The Wire’ — that opened up our tolerance for those types of characters,” he says. “Maybe it’s just the evolution of good storytelling. More complex, real characters.”

In each episode of “The Following,” Bacon’s character must outwit Purefoy’s character to determine the identity of the next victim. “You will see sides of Carroll that are endearing and charming and boyish and a bit lost,” Purefoy says. “And then you will see sides that are monstrous and bat-s- – t crazy.” He also predicts the series will be a game-changer for network television. “This is a show that I’ve likened to a crochet needle going into your stomach and tugging gently on your entrails,” he says.

The graphic content on “The Following” includes a woman who commits suicide with an ice pick and a victim who is burned alive. And it’s very likely that this kind of gore will be viewed differently after the Dec. 14 Sandy Hook Elementary School shooting in Newtown, Conn., which left 20 children and six adults dead.

Siega, who lives in New York, was rattled by the Newtown shooting. “What happened in Connecticut was horrendous. I have three young kids — I can’t even think about that sort of thing,” he says. He says that he and the show’s writers make stories to “drive these plots forward and create drama on television.” But as far as whether the show puts too much violence out there, he adds, “I certainly hope we’re not doing that.”

At the recent Television Critics Association press tour, Fox Entertainment chairman Kevin Reilly defended the show’s content. “We’re not glorifying serial killers,” he said. “Clearly, there is an appetite. People like these things.”

Reilly’s conviction is best illustrated in the new BBC eight-part series about one of the most popular killers of all time — Jack the Ripper. The dark, dank alleys of London provide the backdrop on “Ripper Street,” which uses a mix of real and fictional characters. “You walk through the East End of London today, 120 years later, and there are three or four tour guides at any one time taking groups of people down the streets where he killed the women,” says the show’s creator Richard Warlow.

What’s especially potent for this narrative is that Jack the Ripper was never caught. “There’s just this black hole where an identity should be,” Warlow says.

Maybe the appeal of these serial killer shows is that viewers know everyone has something to hide. “Often the dark secrets are in the people when you’re walking along, you know, 10th Avenue in New York,” says Purefoy. “I’m looking around, wondering, ‘Who’s got the dark secrets here?’” he says. “People have those; we all have secrets of some kind.”

THE FOLLOWING

Monday, 9 p.m., Fox

RIPPER STREET

Saturday, 9 p.m., BBC America

IN THE WORKS

Other shows in development without premiere dates include:

* An FX pilot, “The Bridge,” which began filming in Texas last fall, depicts American and Mexican detectives tracking a killer across the borders. Diane Kruger will star.